CVE-2026-63877

In the Linux kernel, the following vulnerability has been resolved:

serial: dz: Convert to use a platform device

Prevent a crash from happening as the first serial port is initialised:

  Console: switching to colour frame buffer device 160x64
  tgafb: SFB+ detected, rev=0x02
  fb0: Digital ZLX-E1 frame buffer device at 0x1e000000
  DECstation DZ serial driver version 1.04
  CPU 0 Unable to handle kernel paging request at virtual address 000000bc, epc == 8048b3a4, ra == 80470a78
  Oops[#1]:
  CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.19.0-dirty #35 NONE
  $ 0   : 00000000 1000ac00 00000004 804707ac
  $ 4   : 00000000 80e20850 80e20858 81000030
  $ 8   : 00000000 8072c81c 00000008 fefefeff
  $12   : 6c616972 00000006 80c5917f 69726420
  $16   : 80e20800 00000000 808f8968 80e20800
  $20   : 00000000 807f5a90 808b0094 808d3bc8
  $24   : 00000018 80479030
  $28   : 80c2e000 80c2fd70 00000069 80470a78
  Hi    : 00000004
  Lo    : 00000000
  epc   : 8048b3a4 __dev_fwnode+0x0/0xc
  ra    : 80470a78 serial_base_ctrl_add+0xa0/0x168
  Status: 1000ac04	IEp
  Cause : 30000008 (ExcCode 02)
  BadVA : 000000bc
  PrId  : 00000220 (R3000)
  Modules linked in:
  Process swapper/0 (pid: 1, threadinfo=(ptrval), task=(ptrval), tls=00000000)
  Stack : 00400044 00400040 8046f4cc 00000000 808a6148 808a0000 808f8968 8086983c
          808e0000 8046fc84 1000ac01 00000028 80e20700 802ba3f8 80e20700 80d34a94
          80c1b900 80e20700 80e20700 80e20700 80e20700 80444650 00000000 00000000
          00000000 807f5a90 808b0094 80447080 00400040 808e0000 80d34a94 808a6148
          80d34a94 00000004 80e20700 00000000 8076974c 80469810 80c2fe3c 1000ac01
          ...
  Call Trace:
  [<8048b3a4>] __dev_fwnode+0x0/0xc
  [<80470a78>] serial_base_ctrl_add+0xa0/0x168
  [<8046fc84>] serial_core_register_port+0x1c8/0x974
  [<808c6af0>] dz_init+0x74/0xc8
  [<800470e0>] do_one_initcall+0x44/0x2d4
  [<808b111c>] kernel_init_freeable+0x258/0x308
  [<8072e434>] kernel_init+0x20/0x114
  [<80049cd0>] ret_from_kernel_thread+0x14/0x1c

  Code: 27bd0018  03e00008  2402ffea <8c8200bc> 03e00008  00000000  27bdffc0  afbe0038  afb30024

  ---[ end trace 0000000000000000 ]---

-- where a pointer is dereferenced that has been derived from a null
pointer to the port's parent device.

Since no device is available with legacy probing and it's not anymore a
preferable way to discover devices anyway, switch the driver to using a
platform device and use it as the port's parent device.  Update resource
handling accordingly and only request the actual span of addresses used
within the slot, which will have had its resource already requested by
generic platform device code.

Use platform_driver_probe() not just because the DZ device is fixed with
solder on board and not straightforward to remove, but foremost because
the associated TTY's major device number is the same as used by the zs
driver and the first driver to claim it will prevent the other one from
using it.  Either one DZ device or some SCC devices will be present in a
given system but never both at a time, and therefore we want the major
device number to be claimed by the first driver to actually successfully
bind to its device and platform_driver_probe() is a way to fulfil that.

An unfortunate consequence of the switch to a platform device is we now
hand the console over from the bootconsole much later in the bootstrap.
The firmware console handler appears good enough though to work so late
and in particular with interrupts enabled.

Conversely only starting the console port so late lets the reset code
fully utilise our delay handlers, so switch from udelay() to fsleep()
for transmitter draining so as to avoid busy-waiting for an excessive
amount of time.